Method for repairing copper diffusion barrier layers on a semiconductor solid substrate and repair kit for implementing this method

ABSTRACT

Method for repairing copper diffusion barrier layers on a semiconductor solid substrate and repair kit for implementing this method. 
     One subject of the present invention is a method for repairing a surface of a substrate coated with a discontinuous copper diffusion barrier layer of a titanium-based material. 
     According to the invention, this method comprises:
         a) the contacting of the surface with a suspension containing copper or copper alloy nanoparticles for a time of between 1 s and 15 min; and   b) the contacting of the thus treated surface with a liquid solution having a pH of between 8.5 and 12 and containing:
           at least one metal salt,   at least one reducing agent,   at least one stabilizer
 
at a temperature of between 50° C. and 90° C., preferably between 60° C. and 80° C., for a time of between 30 s and 10 min, preferably between 1 min and 5 min, in order to thus form a metallic film having a thickness of at least 50 nanometers re-establishing the continuity of the copper diffusion barrier layer.

The present invention relates in general to a method for repairing asurface of a substrate, especially that of a semiconductor substratewhich may or may not bear an insulating layer, said substrate beingcoated with a discontinuous copper diffusion barrier layer, defining thesurface to be repaired.

The invention is essentially applicable in the field of microelectronicsfor the metallization, in particular with copper, of through vias (alsocalled through silicon vias or through wafer vias or through waferinterconnects) which are keystones for three-dimensional (3D) orvertical integration of electronic chips or dies. The invention is alsoapplicable in other fields of electronics in which a substrate havingthrough vias that are covered with an insulating layer and with adiscontinuous barrier layer must be treated so as to obtain a continuousbarrier layer over the entire surface of the vias. In this context,mention may be made of the fabrication of interconnects in printedcircuits (also called printed circuit boards or printed wiring boards)or the fabrication of passive components, such as inductors, orelectromechanical components in integrated circuits or microsystems(also called microelectromechanical systems).

Current electronic systems are made up for the most part from severalintegrated circuits, or components, and each integrated circuit fulfilsone or more functions. For example, a computer comprises at least onemicroprocessor and several memory circuits. Each integrated circuitusually corresponds to an electronic chip in its own package. Theintegrated circuits are soldered to or plugged into, for example, aprinted circuit board or PCB, which ensures connection between theintegrated circuits.

The continual need to increase the functionality density of electronicsystems has led to a first approach of the “system-on-chip” concept, allthe components and circuit blocks needed to carry out all the functionsof the system then being produced on the same chip, without using thesupport of a printed circuit. In practice, it is nevertheless verydifficult to obtain a high-performance “system on chip” since theprocesses for fabricating logic and memory circuits for example differvery substantially. The “system-on-chip” approach has therefore led toaccepting compromises as regards the performance of the variousfunctions carried out on the same chip. In addition, the size of suchchips and their fabrication yield have reached the limits of theireconomic feasibility.

A second approach consists in fabricating, in the same package, a moduleproviding the interconnection of several integrated circuits, which maythen derive from the same semiconductor substrate or from differentsubstrates. The package thus obtained or MCM (multichip module) thustakes the form of a single component. This MCM approach makes itpossible to obtain a higher interconnection density and therefore betterperformance than the conventional PCB approach. However, it is notfundamentally different therefrom. Apart from the size and weight of thepackage, the performance of an MCM remains limited by parasitic elementsassociated with the length of the connections from the substrate andwith the wire bonding connecting the substrate or the chips to the pinsof the package.

A third approach called “three-dimensional (3D) integration” or“vertical integration” is characterized by the fact that the chips aresuperposed and connected together by vertical interconnects. The stackobtained thus comprises several layers or strata of active components orchips and constitutes a 3D integrated circuit or 3D IC.

The benefits of 3D integration stem simultaneously:

(1) from the improvement in performance, e.g. the reduction inpropagation time and in the dissipated power, the increase in operatingspeed of the system combined with faster communication between thefunctional blocks, the increase in bandwidth for each functional block,and the greater immunity to noise;

(2) from the improvement in costs, e.g. increase in integration density,better fabrication yield, thanks to the use of the electronic chipgeneration most suitable to each functional block, and improvement inreliability; and

(3) from the possibility of producing highly integrated systems by thestacking of heterogeneous technologies (also called co-integration),i.e. involving various materials and/or various functional components.

Thus, 3D integration constitutes today an indispensable alternative tothe conventional approaches, which have reached their limits in terms ofperformance, functionality diversification and production cost. Thebasic principles and advantages of 3D integration have been describedfor example by A. W. Topol, D. C. La Tulipe, L. Shi, D. J. Frank, K.Bernstein, S. E. Steen, A. Kumar, G. U. Singco, A. M. Young, K. W.Guarini and M. Leong in “Three-dimensional integrated circuits”, IBMJournal Res. & Dev., Vol. 50, No. 4/5, July/September 2006, pages491-506.

After the chips have been stacked, for example by bonding them together,they may be individually connected to the pins of the package by wirebonding. The chips may generally be interconnected by employing throughvias.

Thus, the elementary technologies needed to produce three-dimensionalintegrated circuits comprise in particular the thinning of siliconwafers, the alignment between the layers, the bonding of the layers, andthe etching and metallization of the through vias within each layer.

Silicon wafers may be thinned before the through vias are fabricated(e.g. U.S. Pat. No. 7,060,624 and U.S. Pat. No. 7,148,565).

Alternatively, the vias may be etched and metallized before the siliconwafer is thinned (e.g. U.S. Pat. No. 7,060,624 and U.S. Pat. No.7,101,792). In this case, closed or “blind” vias are etched in thesilicon and then metallized down to the desired depth before the siliconwafer is thinned, so as to obtain through vias.

The good electrical conductivity of copper and its high resistance toelectromigration, i.e. the small amount of copper atoms that migrateunder the effect of the electric current density, which can be animportant cause of failure, make copper in particular a material ofchoice for metallizing the through vias.

The through vias of 3D integrated circuits are generally produced in amanner similar to the “damascene” process used in the microelectronicsfield for the fabrication of interconnects in integrated circuits, in asuccession of steps comprising:

-   -   etching of the vias in or through the silicon wafer;    -   deposition of an insulating dielectric layer;    -   deposition of a barrier layer or liner, serving to prevent the        migration or diffusion of copper;    -   filling of the vias by copper electrodeposition; and    -   removal of the excess copper by mechanico-chemical polishing.

The barrier layer, because of the high resistivity of the materialsconstituting it, generally has too high a resistance to allow, by directelectrochemical means, a homogeneous or uniform film of copper to bedeposited on the scale of the wafer, a phenomenon known to those skilledin the art as ohmic drop.

It is therefore generally necessary, prior to the step of filling bycopper electrodeposition, to cover the barrier layer with a thinmetallic copper layer, called a seed layer.

This seed layer may be produced in various ways: by PVD (physical vapordeposition) or CVD (chemical vapor deposition) or by deposition inliquid medium using what is called electrografting technology.

The insulating dielectric layer may be inorganic (generally consistingof silicon dioxide SiO₂, silicon nitride SiN or aluminum oxide, forexample), deposited by CVD or another process, or may be organic(parylene C, N or D, polyimide, benzocyclobutene or polybenzoxazole forexample) deposited by dipping in a liquid medium, or using the SOG(spin-on-glass) method.

The deposition of this insulating layer is followed by the deposition ofa copper diffusion barrier layer by vapor phase deposition (PVD, CVD orALD), said layer generally consisting of tantalum (Ta), titanium (Ti),tantalum nitride (TaN), titanium nitride (TiN), a titanium-tungstenalloy (TiW), tungsten carbonitride (WCN) or a combination of thesematerials, for example.

Chemical vapor deposition (CVD or ALD) used to deposit the copperdiffusion barriers makes it possible to obtain a conformal barrierlayer, i.e. one that faithfully matches the topography of the surface tobe coated, and to do so for a wide range of aspect ratios defined by theratio of the depth of the via to the diameter of the via. However, whenaspect ratios become too high, for example greater than 5/1, for examplearound 10/1, the thickness at the bottom of the vias of the barrierlayers deposited by CVD becomes too small and results in the formationof local discontinuities. This phenomenon causes the barrier propertiesto drop in discontinuous zones.

Physical vapor deposition (PVD), which is itself also used fordepositing copper diffusion barriers, can be used only in structureshaving a very low aspect ratio (around 3/1). This is because thethickness of the coating deposited by PVD is directly proportional tothe solid angle seen from the surface to be coated. Therefore, thoseparts of the surface having salient angles are covered with a thickerlayer than those parts of the surface having reentrant angles. As aresult, the copper diffusion barrier layers formed by physical vapordeposition are not conformal and therefore do not have a uniformthickness at all points on the surface of the substrate.

High-density three-dimensional integrated circuits require the use ofanisotropic silicon etching processes so as to obtain vias with avertical profile. The anisotropic etching of silicon (e.g. U.S. Pat. No.5,501,893) usually results in a bowed, rough and striated or scallopedprofile. Thus, the sidewalls of the vias may in part be not covered, orcovered with an insufficient thickness of barrier layer, thereforegiving rise to energy dissipation problems due to the diffusion ofcopper into the insulator and also to less reliable performances.

These drawbacks make it very challenging to produce a perfectlycontinuous barrier layer suitable for metallizing the through vias ofhigh-density three-dimensional integrated circuits, in which the viasmay have high aspect ratios.

Under these conditions, the object of the present invention is to solvethis new technical problem by providing a novel method for repairingdiscontinuous copper diffusion barrier layers present on the surface ofa substrate, especially a semiconductor substrate or a semiconductorsubstrate having an insulating layer, such as in particular a wafer of asilicon-based material which may or may not have an insulating layer.This novel method is intended in particular for repairing discontinuouscopper diffusion barrier layers present on the surface of a substratehaving a “through via”-type structure intended for the production ofinterconnects in integrated circuits, in particular in 3D integratedcircuits.

Within the context of the present invention, the expression“discontinuous copper diffusion barrier layer” is understood to mean alayer made of a material that prevents the migration of copper andhaving either holes or zones of very small thickness through which thecopper may migrate. The discontinuity of the copper diffusion barrierlayer therefore constitutes a functional discontinuity, the cause ofwhich is, nevertheless, a structural discontinuity in most cases (a holein the layer).

It has been discovered, and this constitutes the basis of the presentinvention, that it is possible to solve the aforementioned technicalproblem, in a completely satisfactory manner on an industrial scale, bytreating the surface to be repaired using an electroless processemploying very specific chemical compositions.

Completely surprisingly and unexpectedly, it has also been discoveredthat these specific compositions make it possible not only toreestablish the functionality of a copper diffusion barrier layer overthe entire surface of the substrate, including in discontinuous zones ofthe initial layer, but also to obtain significant improvements notforeseeable to those skilled in the art in terms of adhesion andconformity of the copper layers deposited electrochemically on thesurfaces repaired using these compositions.

Thus, one subject of the present invention is a method for repairing asurface of a substrate, especially a semiconductor substrate or asemiconductor substrate bearing an insulating layer, said substratebeing coated with a discontinuous copper diffusion barrier layer of atitanium-based material defining said surface to be repaired, whichcomprises:

a) the contacting of said surface with a suspension containing copper orcopper alloy nanoparticles for a time of between 1 s and 15 min, thuscausing the nanoparticles to be selectively adsorbed onto the surface ofthe barrier layer; and

b) the contacting of the thus treated surface with a liquid solutionhaving a pH of between 8.5 and 12, preferably between 9 and 11, andcontaining:

-   -   at least one metal salt, preferably a nickel salt or a salt of a        nickel alloy,    -   at least one reducing agent, preferably a boron compound, and    -   at least one stabilizer        at a temperature of between 50° C. and 90° C., preferably        between 60° C. and 80° C., for a time of between 30 s and 10        min, preferably between 1 min and 5 min, in order to thus form a        metallic film having a thickness of at least 50 nanometers        re-establishing the continuity of the copper diffusion barrier        layer.

According to one particular feature of the invention, prior to theaforementioned step a), a treatment of said surface enabling theimpurities present to be removed may be carried out, such as inparticular washing with a solution based on aqueous ammonia and hydrogenperoxide, followed by rinsing with water.

According to another particular feature of the invention, prior to theaforementioned step b), the treated surface obtained after step a) maybe rinsed with water.

As seen above, the substrate, the surface of which is intended to berepaired according to the invention, is preferably a semiconductorsubstrate which may or may not be coated with an insulating layer, andin particular a substrate having a number of through vias, such as thoseused for the fabrication of three-dimensional integrated circuits.

Within the context of the present invention, the material constitutingthe copper diffusion barrier layer is a titanium-based material. Thismaterial may be substantially pure titanium or a titanium alloy such as,in particular, titanium nitride (TiN), a titanium-tungsten alloy (TiW)or titanium silicon nitride (TiSiN).

The method according to the present invention is essentiallycharacterized in that it comprises two essential steps a) and b), eachof them involving a specifically selected composition.

In a completely novel manner, the first step of this method uses asuspension containing copper or copper alloy nanoparticles. It has beenobserved that such particles have a particularly high affinity with thetitanium-based material constituting the copper diffusion barrier layer,this affinity being manifested by selective adsorption of thenanoparticles onto the surface of the barrier layer, with the exceptionof the discontinuity zones.

In general, the aforementioned nanoparticles have an average size ofless than 25 nanometers and more preferably less than 10 nanometers.

The suspensions (or colloidal solutions) containing these nanoparticlesmay be produced in a manner known per se, by reaction, in the presenceof a surfactant-type stabilizer, such as cetyltrimethylammonium bromide(CTMAB), between a copper precursor, in particular copper sulfate, and areducing agent such as, for example, sodium borohydride. Suchsuspensions contain the zerovalent copper or copper alloy particles incolloidal form.

Among copper alloys that can be used for the preparation of a suspensionsuitable for step a), mention may in particular be made of copper-nickelalloys and copper-cobalt alloys.

The nanoparticles are generally present, within the suspension, in anamount of between 0.1 g/l and 10 g/l and preferably between 3 g/l and 6g/l. The nanoparticles are stabilized using methods widely described inthe literature, in such a way that the amount of stabilizer used isbetween 5 g/l and 100 g/l and preferably between 30 g/l and 50 g/l. Theamount of reducing agent used under these conditions is generallybetween 0.5 g/l and 10 g/l and preferably between 2 g/l and 5 g/l.

The nanoparticles may be selectively adsorbed onto the surface of thetitanium-based discontinuous barrier layer by simple contacting of thesurface with the suspension containing the copper or copper alloynanoparticles for a relatively short time, which may be between 1 s and15 min and preferably between 10 s and 5 min.

The copper or copper alloy nanoparticles thus selectively adsorbed ontothe surface of the titanium-based barrier layer make it possible,completely unexpectedly, for a metal film (other than a copper film) tobe subsequently formed and for the barrier layer to be repaired.

This metal film may be produced by an electroless process, constitutingstep b) of the method according to the invention.

For this purpose, the surface of the barrier layer containing the copperor copper alloy nanoparticles is brought into contact, optionally afterrinsing it with water, with a liquid solution as defined above underconditions for forming a film having a thickness of at least 50nanometers.

The thickness of the film formed essentially depend:

-   -   on the one hand, on the qualitative and quantitative nature of        the liquid treatment solution; and    -   on the other hand, on the duration of the aforementioned        contacting and on the temperature of the solution.

In general, this step b) will be carried out at a temperature of between50° C. and 90° C., preferably between 60° C. and 80° C., for a time ofbetween 30 s and 10 min, and preferably between 1 min and 5 min.

Excellent results have been obtained using a liquid solution thatcomprises, in a protic, preferably aqueous, solvent:

-   -   1 g/l to 40 g/l, and preferably 20 g/l to 30 g/l, of a metal        salt, preferably a nickel salt or a salt of a nickel alloy;    -   0.5 g/l to 10 g/l, and preferably 2 g/l to 3 g/l, of a reducing        agent, preferably a boron compound; and    -   20 g/l to 100 g/l, and preferably 50 g/l to 70 g/l, of a        stabilizer.

With such a solution, used within the aforementioned general temperaturerange, a metallic film is obtained that has a thickness of between 50and 200 nanometers for a contacting time of between 1 min and 4 min.

Advantageously, the metal salt, which must be a salt other than a coppersalt, is selected from nickel sulfate, nickel chloride, nickel acetateand nickel sulfamate.

The reducing agent used in the solution employed in step b) isadvantageously selected from boron derivatives and in particular fromdimethyl-aminoborane, sodium borohydride, pyridine borane, morpholeneborane and tert-butylamine borane. Preferably, dimethylaminoborane(DMAB) is used.

There is no particular limitation as regards the stabilizer used in thesolution employed in step b). This stabilizer is generally selected fromthe group constituted of ethylenediamine and salts, especially alkalimetal or ammonium salts, of acetic, succinic, malonic, aminoacetic,malic or citric acids. Preferably, sodium citrate or tetramethylammoniumcitrate is used.

The solution employed in step b) generally has a pH of between 8.5 and12, preferably between 9 and 11. For this purpose, the pH of thesolution may be adjusted, in particular by adding a base such as sodiumhydroxide.

The method that has been outlined above makes it possible to repair atitanium-based copper diffusion barrier layer having discontinuities.

In addition, this method may be employed for repairing any type ofsurface and in particular surfaces having high aspect ratios, such asthe surface of through vias used for producing interconnects inintegrated circuits.

Completely surprisingly and unexpectedly, it has been observed that thebarrier layer thus repaired promotes the subsequent adhesion of a copperlayer electrochemically deposited on said barrier after repair, theadhesion to a “repaired” barrier layer being greater than the adhesionmeasured on the same barrier layer but not repaired.

It has also been observed, completely unpredictably, that the method ofrepair described above results in a significant increase in theconformity of the copper layers subsequently depositedelectrochemically.

According to a second aspect, an object of the present invention is arepair kit for repairing a surface of a substrate, especially asemiconductor substrate or a semiconductor substrate bearing aninsulating layer, said substrate being coated with a discontinuouscopper diffusion barrier layer consisting of a titanium-based material,defining said surface to be repaired, which comprises:

-   -   on the one hand, a suspension containing copper or copper alloy        nanoparticles, a stabilizer and a reducing agent; and    -   on the other hand, a liquid solution having a pH of between 8.5        and 12, preferably between 9 and 11, and containing:    -   at least one metal salt, preferably a nickel salt or a salt of a        nickel alloy,    -   at least one reducing agent, preferably a boron compound, and        -   at least one stabilizer.

According to one particular feature, the aforementioned suspensioncontains:

-   -   copper or copper alloy nanoparticles, in an amount of between        0.1 g/l and 10 g/l, and preferably between 3 g/l and 6 g/l;    -   a stabilizer, in an amount of between 5 g/l and 100 g/l and        preferably between 30 g/l and 50 g/l; and    -   a reducing agent in an amount of between 0.5 g/l and 10 g/l, and        preferably between 2 g/l and 5 g/l.

According to another particular feature, the aforementioned liquidsolution comprises, in a protic, preferably aqueous, solvent:

-   -   1 g/l to 40 g/l, and preferably 20 g/l to 30 g/l, of a metal        salt, preferably a nickel salt or a salt of a nickel alloy;    -   0.5 g/l to 10 g/l, and preferably 2 g/l to 3 g/l, of a reducing        agent, preferably a boron compound; and    -   20 g/l to 100 g/l, and preferably 50 g/l to 70 g/l, of a        stabilizer.

EXAMPLES

The invention will be better understood on reading the description ofthe following nonlimiting examples, with reference to the appendedfigures which show, respectively:

FIG. 1: SEM (scanning electron microscopy) micrograph of the surface ofa TiN barrier layer obtained by PVD, after being contacted with asolution of copper nanoparticles according to step 1 of example 1.

FIG. 2: SEM micrograph of the surface of a TiN barrier layer obtained byPVD, after deposition of an NiB layer initiated by the coppernanoparticles according to step 2 of example 1.

FIG. 3: SEM micrograph of the surface of an unrepaired discontinuous TiWbarrier layer obtained by PVD in through vias.

FIG. 4: SEM micrograph of the surface of a discontinuous TiW barrierlayer repaired by depositing an NiB layer according to example 2.

FIG. 5: Schematic representation of the pulsed galvanostatic protocolused to form a copper seed layer on the various barrier layers.

FIG. 6: SEM micrograph of the surface of through vias, said surfacebeing coated with a discontinuous TiW barrier layer obtained by PVD,untreated and treated according to example 2 and then coated with acopper seed layer.

FIG. 7: SEM micrograph of the surface of a discontinuous TiN barrierlayer obtained by MOCVD in through vias.

FIG. 8: SEM micrograph of the surface of through vias, said surfacebeing coated with a TiN barrier layer obtained by MOCVD, untreated andtreated according to example 3 and then coated with a copper seed layer.

FIG. 9: SEM micrograph of the surface of a discontinuous Ti barrierlayer obtained by PVD in through vias.

FIG. 10: SEM micrograph of the surface of through vias, said surfacebeing coated with a Ti barrier layer obtained by PVD, untreated andtreated according to example 4 and then coated with a copper seed layer.

The following examples were produced on a laboratory scale. In theseexamples, the following abbreviations are used:

-   -   Ti: titanium    -   TiN: titanium nitride    -   TiW: titanium-tungsten alloy    -   PVD: physical vapor deposition    -   CVD: chemical vapor deposition    -   MOCVD: metal-organic chemical vapor deposition (by means of an        organometallic compound)    -   NH₄OH: ammonium hydroxide    -   CuSO₄: copper sulfate    -   CTAB: cetyltrimethylammonium bromide    -   NiSO₄: nickel sulfate    -   TMAH: tetramethylammonium hydroxide    -   DMAB: dimethylaminoborane.

Unless otherwise indicated, these examples were produced under standardtemperature and pressure conditions (about 25° C. at 1 atmosphere) inthe ambient air, and the reactants used were commercially obtainedwithout any additional purification.

Example 1 Formation of a Nickel-Boron Layer on a TiN Barrier Depositedby PVD

This example was produced on a blanket titanium nitride (TiN) substratehaving no discontinuity, so as to check the formation of a nickel-boronmetal layer on this type of surface.

Substrate:

The substrate used in this example was a silicon coupon with sides of 4cm (4×4 cm) and a thickness of 750 μm, covered by PVD with TiN having athickness of 40 nm and a resistivity of 184 μΩ·cm.

Surface Treatment:

Before use, the TiN surfaces were cleaned in a 30% NH₄OH/35% H₂O₂/H₂Omixture in a 1/1/10 volume ratio. The specimen was immersed for oneminute in the solution, which was subjected to ultrasound. It was thenrinsed freely with water.

Barrier Repair:

A nickel-boron (NiB) barrier was deposited in two steps on the surfaceof the substrate according to the protocol below:

Step 1: Activation of the Surface by Cooper Nanoparticles:

Solution:

A colloidal suspension of copper nanoparticles was prepared at 20° C. Todo this, 250 mg of a CuSO₄.5H₂O (10 mol) metal precursor were dissolvedin 50 ml of deionized water and then 1.8 g of a stabilizer, CTAB (8×10⁻²mol), were added to this solution. Next, 2 ml of a sodium borohydridesolution (100 mg, 5×10⁻² mol) were added to this solution in a singleinjection. The solution immediately changed color, becoming red/blackcharacteristic of the zerovalent metal present in colloidal form.

Protocol:

The titanium nitride (TiN) substrate was placed in the colloidalsuspension of copper nanoparticles prepared beforehand. The specimen waskept in this solution for a time of about 2 minutes and then rinsed withdeionized water for a time of about 1 minute, before being dried in astream of argon.

Characterization:

Scanning electron microscopy (SEM) analysis (see FIG. 1) was used toreveal the distribution of copper nanoparticles on the surface of thesubstrate.

Step 2: Formation of a Nickel Layer by Electroless Deposition:

Solution:

The solution used in this example was prepared by pouring, into a pyrexbeaker, 50 ml of deionized water, 1.41 g of NiSO₄ (0.1M), 2.98 g oftribasic sodium citrate (0.2M) and 141 mg of DMAB (5×10⁻²M). The pH ofthe solution was adjusted to 9 by the addition of a 0.1M NaOH (sodiumhydroxide) or 0.1M TMAH solution.

Protocol:

The solution was kept at 70° C. in a water bath and then the specimenprepared in step 1 was placed in the medium for a time of about 2minutes. The substrate was then removed, rinsed with deionized water anddried in a stream of argon.

Characterization:

The surface thus treated was characterized by a uniform metallic(mirror) appearance.

The metal thickness obtained was about 100 nm.

SEM analysis (see FIG. 2) was used to demonstrate the formation of acontinuous NiB metal film over the entire surface.

Example 2 Repair of a Discontinuous TiW Barrier Having Through Vias

Substrate:

The substrate used in this example consists of a silicon wafer havingsides of 4 cm (4×4 cm) and a thickness of 750 μm, said wafer beingetched with cylindrical features of the “through via” type 120 μm indepth and 40 μm in diameter. This substrate was covered with a layer oforganic polymer insulator having a thickness of about 2 μm on the wallsof the via and about 8 μm on its surface, the bottom surface of the viabeing free of insulator. This assembly was itself covered by PVD with aTiW barrier layer ranging in thickness from 100 nm to 150 nm and havingmany holes in the lower part of the via walls (see FIG. 3).

Surface Treatment:

This type of substrate required no prior surface treatment.

Barrier Repair:

This step was carried out in the same way as that described inexample 1. However, attachment of the nanoparticles required thespecimen to be immersed in the suspension of nanoparticles for oneminute in an ultrasonic bath.

Characterization:

The same uniform metallic (mirror) appearance as in example 1 wasobserved.

SEM analysis (see FIG. 4) was used to demonstrate the formation of acontinuous NiB metal film over the entire surface.

Formation of a Copper Seed Layer:

To demonstrate the effectiveness of the above repair, a copper seedlayer was deposited on the repaired barrier using the followingoperating method:

Solution:

A copper seed layer was deposited using an aqueous electroplatingsolution containing 2.1 ml/l (32 mM) of ethylenediamine and 4 g/l (16mM) of CuSO₄.5H₂O.

Protocol:

The electroplating process used in this example comprised variousconsecutive steps:

a) a “cold entry” step in which the substrate was brought into contact,by immersion, without being electrically supplied, with theelectroplating solution for a time of at least one minute (for example,3 minutes);

b) a copper growth step in which the substrate is cathodically biased inpulsed galvanostatic mode while simultaneously being rotated at a speedof 20 to 100 rpm (for example, 40 rpm).

FIG. 5 shows in detail the pulsed galvanostatic protocol that can beused, with a total period P of between 10 ms and 2 s (0.6 s in theexample), an on-time T_(ON) of between 2 ms and 1.6 s (0.35 s in theexample), during which a current per unit area of generally between 0.6mA·cm⁻² and 10 mA·cm⁻² (2.77 mA·cm⁻² in the example) is imposed, and anoff-time T_(OFF) with no bias of between 2 ms and 1.6 s (0.25 s in theexample).

The duration of this step depends, as it will be understood, on thedesired thickness of the seed layer. This duration can be easilydetermined by a person skilled in the art, the growth of the film beingdependent on the charge passed through the circuit. Under theaforementioned conditions, the deposition rate was about 1.5 nm percoulomb of charge passed through the circuit, thereby giving a durationof the electroplating step of around 17 minutes in order to obtain acoating having a thickness of 300 nm; and

c) a “hot exit” step in which the copper-coated substrate was removedfrom the electroplating solution at zero rotation speed while being keptunder voltage bias. The duration of this phase was about 2 seconds.

The rotation speed was then increased to 500 rpm for 10 seconds, thecathodic bias being cut off during this last phase. The substrate wasthen rinsed with deionized water and dried in a stream of nitrogen.

Characterization:

SEM analysis (see FIG. 6) was used to demonstrate the stack of thethree, TiW/NiB/copper, layers over the entire surface of the via beforeand after repair.

Example 3 Repair of a TiN Barrier on a Silicon Surface Having ThroughVias, Followed by Deposition of a Copper Seed Layer

In order for the effectiveness of the repair to be precisely displayed,a copper seed layer was deposited on a substrate having through vias,either immediately or after the repair step.

Substrate:

The substrate used in this example consisted of a silicon wafer withsides of 4 cm (4×4 cm) and a thickness of 750 μm, said wafer beingetched with cylindrical features of the “through via” type 100 μm indepth and 10 μm in diameter. An insulator (SiO₂) first layer having athickness of 0.5 μm was present. This layer was covered with a TiNbarrier of about 75 nm deposited by MOCVD, but not reaching the bottomand the lower part of the walls of the via (see FIG. 7).

Surface Treatment:

This step was carried out in the same way as that described in example1.

Barrier Repair:

This step was carried out in the same way as that described in example2.

Formation of a Copper Seed Layer:

This step was carried out in the same way as that described in example2.

Characterization:

SEM analysis (see FIG. 8) was used to demonstrate the stack of thethree, TiN/NiB/copper, layers over the entire surface of the via withand without repair.

Example 4 Repair of a Ti Barrier on a Silicon Surface Having ThroughVias, Followed by Deposition of a Copper Seed Layer

Substrate:

The substrate used in this example consists of a silicon wafer havingsides of 4 cm (4×4 cm) and a thickness of 750 μm, said wafer beingetched with cylindrical features of the “through via” type 120 μm indepth and 35 μm in diameter. A Ti barrier layer was deposited by PVD.This layer had a thickness that dropped very rapidly, becoming less than5 nm from a depth of 80 μm onwards in the via (see FIG. 9).

Surface Treatment:

This step was carried out in the same way as that described in example1.

Barrier Repair:

This step was carried out in the same way as that described in example2.

Formation of a Copper Seed Layer:

This step was carried out in the same way as that described in example2.

Characterization:

SEM analysis (see FIG. 10) was used to demonstrate the stack of thethree, Ti/NiB/copper, layers over the entire surface of the via with andwithout repair.

The measurements of the copper seed layer thicknesses over the entiresurface of a via showed a significant increase in the conformity of thelayers after repair. The measured copper thicknesses at the bottom of avia thus increased from 38 nm without repair to 154 nm after repair forcopper thicknesses of about 350 nm at the top of the via.

Example 5 Measurement of the Adhesion of a Copper Seed Layer DepositedElectrochemically on a TiN Barrier with and without Repair

The substrate used in this example was the same as that used in example1.

A copper seed layer was deposited on several specimens according to theprotocol described in example 2.

A first series of copper layers were deposited on unrepaired TiNbarriers followed by a second series on TiN barriers after repair.

The results obtained are given in table 1.

TABLE 1 Measurement of the adhesion of a copper seed layer depositedelectrochemically on a TiN barrier with and without repair SubstrateCopper thickness (nm) Adhesion (J/m²) TiN 380 2.3 TiN 370 2.1 TiN 3802.1 TiN after repair 390 7.8 TiN after repair 380 7.9 TiN after repair380 7.9

The results given in table 1 show that the method of repairing the TiNbarrier significantly improves the adhesion of the copper layerelectrochemically deposited on the barrier layer.

It has also been observed that the copper layers obtained exhibitexcellent conformity, greatly superior to that of the copper layersdeposited on the surface of an unrepaired discontinuous barrier layer.

Finally, the method according to the present invention is particularlyadvantageous because it can be carried out entirely in a wet phase,preferably a liquid phase in a protic solvent, and more preferably in anaqueous phase.

1.-11. (canceled)
 12. A method for repairing a surface of a substrate,said substrate being coated with a discontinuous copper diffusionbarrier layer of a titanium-based material defining said surface to berepaired, which comprises: a) contacting said surface with a suspensioncontaining copper or copper alloy nanoparticles for a time of between 1s and 15 min, thus causing the nanoparticles to be selectively adsorbedonto the surface of the barrier layer; and b) contacting the thustreated surface with a liquid solution having a pH of between 8.5 and 12and comprising: at least one metal salt, at least one reducing agent,and at least one stabilizer at a temperature of between 50° C. and 90°C., for a time of between 30 s and 10 min, in order to thus form ametallic film having a thickness of at least 50 nanometersre-establishing the continuity of the copper diffusion barrier layer.13. The method as claimed in claim 12, wherein said substrate is asemiconductor substrate or a semiconductor substrate bearing aninsulating layer.
 14. The method as claimed in claim 12, whichcomprises, prior to the step a), a treatment of said surface enablingimpurities present to be removed.
 15. The method as claimed in claim 14,wherein said treatment of said surface enabling the impurities presentto be removed comprises washing said surface with a solution containinghydrogen peroxide and aqueous ammonia followed by rinsing with water.16. The method as claimed in claim 12, which comprises, prior to thestep b), rinsing the treated surface obtained after step a) with water.17. The method as claimed in claim 14, which comprises, prior to thestep b), rinsing the treated surface obtained after step a) with water.18. The method as claimed in claim 12, wherein the liquid solution usedin the step b) has a pH of between 9 and 11, and comprises: at least onemetal salt, which is a nickel salt or a salt of a nickel alloy, at leastone reducing agent, which is a boron compound, and at least onestabilizer at a temperature of between 60° C. and 80° C., for a time ofbetween 1 min and 5 min.
 19. The method as claimed in claim 18, whichcomprises, prior to the step a), a treatment of said surface enablingthe impurities present to be removed.
 20. The method as claimed in claim18, which comprises, prior to the step b), rinsing the treated surfaceobtained after step a) with water.
 21. The method as claimed in claim12, wherein the liquid solution used in the step b) comprises, in aprotic solvent: 1 g/l to 40 g/l of a metal salt; 0.5 g/l to 10 g/l of areducing agent; and 20 g/l to 100 g/l of a stabilizer.
 22. The method asclaimed in claim 12, wherein the liquid solution used in the step b)comprises, in an aqueous solvent: 20 g/l to 30 g/l, of a metal salt,which is a nickel salt or a salt of a nickel alloy; 2 g/l to 3 g/l, of areducing agent, which is a boron compound; and 50 g/l to 70 g/l of astabilizer.
 23. The method as claimed in claim 12, wherein the metalsalt is selected from the group consisting of nickel sulfate, nickelchloride, nickel acetate and nickel sulfamate.
 24. The method as claimedin claim 18, wherein the metal salt is selected from the groupconsisting of nickel sulfate, nickel chloride, nickel acetate and nickelsulfamate.
 25. The method as claimed in claim 12, wherein the reducingagent is selected from the group consisting of sodium borohydride(NaBH₄), dimethylaminoborane (DMAB), morpholene borane, tert-butylamineborane and pyridine borane.
 26. The method as claimed in claim 18,wherein the reducing agent is selected from the group consisting ofsodium borohydride (NaBH₄), dimethylaminoborane (DMAB), morpholeneborane, tert-butylamine borane and pyridine borane.
 27. The method asclaimed in claim 22, wherein the reducing agent is selected from thegroup consisting of sodium borohydride (NaBH₄), dimethylaminoborane(DMAB), morpholene borane, tert-butylamine borane and pyridine borane.28. The method as claimed in claim 12, wherein the stabilizer isselected from the group consisting of ethylenediamine; alkali metal ofan acid selected from the group consisting of acetic acid, succinicacid, malonic acid, aminoacetic acid, malic acid and citric acid;ammonium salt of an acid selected from the group consisting of aceticacid, succinic acid, malonic acid, aminoacetic acid, malic acid andcitric acid.
 29. The method as claimed in claim 18, wherein thestabilizer is selected from the group consisting of: ethylenediamine;alkali metal of an acid selected from the group consisting of aceticacid, succinic acid, malonic acid, aminoacetic acid, malic acid andcitric acid; ammonium salt of an acid selected from the group consistingof acetic acid, succinic acid, malonic acid, aminoacetic acid, malicacid and citric acid.
 30. The method as claimed in claim 22, wherein thestabilizer is selected from the group consisting of: ethylenediamine;alkali metal of an acid selected from the group consisting of aceticacid, succinic acid, malonic acid, aminoacetic acid, malic acid andcitric acid; ammonium salt of an acid selected from the group consistingof acetic acid, succinic acid, malonic acid, aminoacetic acid, malicacid and citric acid.
 31. The method as claimed in claim 12, wherein thesubstrate is a semiconductor substrate coated with an insulating layerhaving a number of cylindrical features of the “through via” type. 32.The method as claimed in claim 12, wherein the substrate is asemiconductor substrate coated with an insulating layer having a numberof cylindrical features of the “through via” type used for thefabrication of three-dimensional integrated circuits.
 33. A repair kitfor repairing a surface of a substrate, said substrate being coated witha discontinuous copper diffusion barrier layer consisting of atitanium-based material, defining said surface to be repaired, whichcomprises: a suspension containing copper or copper alloy nanoparticles,a stabilizer and a reducing agent; and a liquid solution having a pH ofbetween 8.5 and 12, and comprising: at least one metal salt, at leastone reducing agent, and at least one stabilizer.
 34. The repair kit asclaimed in claim 33, wherein said substrate is a semiconductor substrateor a semiconductor substrate bearing an insulating layer.
 35. The repairkit as claimed in claim 33, wherein the liquid solution has a pH ofbetween 9 and 11, and comprises: at least one metal salt, which is anickel salt or a salt of a nickel alloy, at least one reducing agent,which is a boron compound, and at least one stabilizer.
 36. The repairkit as claimed in claim 33, wherein the suspension comprises: copper orcopper alloy nanoparticles, in an amount of between 0.1 g/l and 10 g/l;a stabilizer, in an amount of between 5 g/l and 100 g/l; and a reducingagent in an amount of between 0.5 g/l and 10 g/l.
 37. The repair kit asclaimed in claim 36, wherein the suspension comprises: copper or copperalloy nanoparticles, in an amount of between 3 g/l and 6 g/l; astabilizer, in an amount of between 30 g/l and 50 g/l; and a reducingagent in an amount of between 2 g/l and 5 g/l.
 38. The repair kit asclaimed in claim 33, wherein the liquid solution comprises, in a proticsolvent: 1 g/l to 40 g/l, of a metal salt; 0.5 g/l to 10 g/l, of areducing agent; and 20 g/l to 100 g/l, of a stabilizer.
 39. The repairkit as claimed in claim 38, wherein the liquid solution comprises, in anaqueous, solvent: 20 g/l to 30 g/l, of a metal salt which is a nickelsalt or a salt of a nickel alloy; 2 g/l to 3 g/l, of a reducing agent,which is a boron compound; and 50 g/l to 70 g/l, of a stabilizer. 40.The repair kit as claimed in claim 33, wherein the reducing agent isselected from the group consisting of sodium borohydride (NaBH₄),dimethylaminoborane (DMAB), morpholene borane, tert-butylamine boraneand pyridine borane.
 41. The repair kit as claimed in claim 33, whereinthe stabilizer is selected from the group consisting of ethylenediamine;alkali metal of an acid selected from the group consisting of aceticacid, succinic acid, malonic acid, aminoacetic acid, malic acid andcitric acid; ammonium salt of an acid selected from the group consistingof acetic acid, succinic acid, malonic acid, aminoacetic acid, malicacid and citric acid.
 42. The repair kit as claimed in claim 33, whereinthe metal salt is selected from the group consisting of nickel sulfate,nickel chloride, nickel acetate and nickel sulfamate.